The Entity-Relationship (ER) model is a high-level conceptual data model that is used to define the data elements and relationships for a specific business domain.
- It is widely used in database design to visually represent the data and its relationships, making it easier to understand and communicate with stakeholders.
ER Diagram (Entity-Relationship Diagram)
An ER Diagram (Entity-Relationship Diagram) is a graphical representation of an entity-relationship model, which is used to visualize the structure of a database.
- It shows the relationships between entities (data objects) and their attributes, and helps in designing the database schema by illustrating the logical structure of the data.
Key Components of ER Model:
1.) Entities:
Entities are objects or things in the real world that are distinguishable from other objects. Each entity has a set of attributes.
- Example: In a university database, entities could be Students, Professors, and Courses.
2.) Attributes:
Attributes are properties or characteristics of an entity.
- Example: For the Student entity, attributes might include StudentID, Name, and DateOfBirth.
3.) Relationships:
Relationships are associations among entities.
- Example: A Student entity might have a relationship with the Course entity, indicating which courses a student is enrolled in.
4.) Keys:
- Primary Key: A unique identifier for each entity instance.
- Foreign Key: An attribute that creates a link between two entities.
5.) ER Diagrams:
- A graphical representation of entities, attributes, and relationships.
Benefits of ER Model:
- Simplifies database design.
- Provides a clear view of the data structure.
- Helps identify entities and relationships.
Introduction to Relational Model
The Relational Model is a type of database model that stores data in tables (relations).
• It is the most widely used data model and forms the foundation for relational database management systems (RDBMS).
Key Components of Relational Model:
1.) Relations (Tables):
- A relation is a table with columns and rows.
- Example: A table named Students with columns for StudentID, Name, and DateOfBirth.
2.) Tuples (Rows):
- A tuple is a single row in a table, representing a single record.
- Example: A row in the Students table representing one student.
3.) Attributes (Columns):
- Attributes are the columns in a table, representing the data fields.
- Example: Columns in the Students table like StudentID, Name, and DateOfBirth.
4.) Domains:
- A domain is the set of allowable values for one or more attributes.
- Example: The domain of the DateOfBirth attribute is valid date values.
5.) Keys:
- Primary Key: A unique identifier for each tuple in a relation.
- Foreign Key: An attribute that creates a link between two relations.
6.) Constraints:
- Rules that ensure the integrity of the data.
- Types: Primary key constraint, foreign key constraint, unique constraint, and check constraint.
Benefits of Relational Model:
- Simplicity: Easy to understand and use.
- Data Integrity: Maintains accuracy and consistency of data.
- Flexibility: Allows complex queries using SQL.
- Scalability: Can handle large amounts of data.
